In the healthy eye, the intra-ocular pressure is maintained between certain physiological limits and these are considered as being normal. In the usual situations, the eye has normal intra-ocular pressures ranging from about 10 to 21 millimeters of mercury. Unfortunately, however, intra-ocular pressure can be abnormally high, and when the eye is harder than normal, this condition is known as glaucoma. Glaucoma is an undesirable condition because the elevated intra-ocular pressure causes damage to the optic nerve located in the back of eyeball. This elevated intra-ocular pressure impairs the circulation to the optic nerve and causes a loss of viable nerve fibers in the optic nerve. Consequently, the function of the optic nerve can be diminished, resulting in a loss of visual function of the eye. The range of increase of intra-ocular pressure can vary from mildly elevated, e.g., about 25 millimeters of mercury and slightly higher, to severe elevation, e.g., within the range from about 60 to 80 millimeters of mercury. Different adverse side effects can occur depending upon how acutely the pressure rises, the magnitude of the pressure elevation, the duration of said elevation in pressure, the underlying condition of the optic nerve and its blood supply, and whether or not the patient is recovering from ocular surgery.
Since elevations in intra-ocular pressure are independent of systemic body blood pressure, intra-ocular pressure elevations are comparatively localized within the eyeball, although the patient may experience systemic symptoms from elevated intra-ocular pressure such as headache, nausea, and vomiting.
Anatomically, the intra-ocular fluid known as aqueous humor is elaborated from the ciliary processes located in the posterior chamber. These ciliary processes are located behind the iris, or the colored part of the eye. Such aqueous humor has a very definite circulatory flow pattern within the eye. This circulatory pathway starts out where the aqueous humor is formed behind the iris. The fluid thus elaborated flows into the anterior chamber through the pupillary aperature of the eye and/or through a surgically created opening in the iris called an iridectomy. The aqueous humor ultimately drains into the angles of the anterior chamber and out through a network of collector channels within the wall of the eye.
The pathway for flow of the aqueous humor will be understood further in reference to the drawings, wherein the circumferential pathways of flow for the aqueous humor are illustrated by directional arrows in the anterior portion thereof.